The present invention relates to a method of measuring the particle content, in particular the soot particle content, in the exhaust gases of an internal combustion engine by means of a sensor arranged in contact with the exhaust gases.
In piston engines, in which the fuel is injected directly into the combustion chamber, such as GDI (Gasoline Direct Injection) engines and diesel engines, problems of soot formation in the exhaust gases occur under certain operating conditions. This is due inter alia to the fact that the air/fuel mixture in the combustion chamber is what is referred to as layered or, more usually, stratified. A further reason for soot formation in the exhaust gases is that, under certain operating conditions, the fuel injected directly into the cylinder strikes the piston and the surrounding cylinder walls. In GDI engines, it is desirable under certain operating conditions to work with a stratified air/fuel mixture because a lower fuel consumption can then be obtained. In order to ignite a lean air fuel/mixture in the combustion chamber using a spark plug, a locally richer mixture must be produced around the region where the spark plug is located. This state with the mixture being divided into a lean and a rich mixture in the combustion chamber is consequently referred to as stratified. The opposite of a stratified air/fuel mixture is a homogeneous air/fuel mixture.
When soot is formed in the exhaust gases, the combustion of the fuel injected into the combustion chamber becomes incomplete, which means that substances that have an effect on the environment are formed in the exhaust gases. In order to prevent soot formation in the exhaust gases, various measures can be taken. For example, the moment of fuel injection can be regulated and/or the moment of ignition of the air/fuel mixture in the combustion chamber can be regulated. It is also possible to regulate the ratio of air to fuel in the air/fuel mixture. However, the problem is detecting when soot formation in the exhaust gases is taking place and how much soot is being formed.
A method and an arrangement for measuring the soot particle content in the exhaust gases of an internal combustion engine are described in DE-A1-33 04 548. An insulator in the form of a ceramic plate is located in the exhaust pipe of the internal combustion engine. Two electrodes are arranged on the insulator at a distance from one another so that a gap is formed between the electrodes. When soot is formed in the exhaust gases, the soot adheres to the ceramic plate between the insulators. The soot then acts as an electric conductor between the electrodes. The quantity of soot on the ceramic plate is proportional to the resistance between the electrodes. The more soot that adheres to the ceramic plate, the smaller the resistance becomes. The resistance can then be measured and an idea of the soot particle content can thus be obtained.
In the case of a GDI engine and a diesel engine which, under certain operating conditions, work with a stratified air/fuel mixture, however, a measurement of the soot particle content in the exhaust pipe does not give an accurate picture of how complete the combustion of the fuel in the combustion chamber is.
One object of the present invention is to provide a method of the type indicated in the introduction which gives a picture of the particle content in the exhaust gases in the combustion chamber of an internal combustion engine.
A further object of the present invention is to provide a method of continuously measuring during operation of the engine the particle content in the exhaust gases in the combustion chamber of an internal combustion engine and, against the background of measurement values obtained, regulating the internal combustion engine so that a lower particle content in the exhaust gases is. obtained.
According to the invention, this is achieved by virtue of the fact that the sensor detects in at least one combustion chamber of the internal combustion engine a quantity, the size of which is dependent on the particle content in the exhaust gases, and that the level of a measurement signal output from the sensor, which signal is dependent on the detected quantity, is determined and compared with a desired value level of a signal which corresponds to a desired particle content in the exhaust gases.
Such a method of measuring the particle content in the exhaust gases provides a true picture of how complete the combustion of the fuel in the combustion chamber is. With a sensor located in the combustion chamber, such as the spark plug of a GDI engine and the heater plug of a diesel engine, simple and economical measuring equipment is obtained for measuring the particle content in the exhaust gases in the combustion chamber in conventional GDI and diesel engines.